Thread: Ground points for charging / jump starting

Originally Posted by BradC

There would be negligible difference in any "inrush of current" between using the battery terminals and using an earth point on the chassis.

The whole "use the chassis" thing comes from the last clamp connected and first clamp disconnected are the ones with greatest potential to cause a spark, so keeping them away from a battery that may be gassing is "a good idea" (tm). Having witnessed a battery that went pop, I can concur with that

That's all it's about.

So can sealed batteries still "gas"?

Originally Posted by gavinwibrow

So can sealed batteries still "gas"?

Absolutely.

So the MF88H "maintenance free" battery in my car has a complex venting system that allows it to breathe whilst minimising water loss.
A true "sealed" battery still has pressure release vents to let it "fart" if it's gassing severely. They are generally a rubber nipple over a spiggot on each cell held under a welded plastic cover. If it generates gas faster than it can recombine it, it'll let it out.

Having blown up a large car battery in my face, I can recommend against it. It sends out a lot of acid that ruins clothes and paintwork. Also, you won’t be hearing much for the following 30 minutes.

Yes I agree, the connecting earth apart from the battery is all about avoiding gas that detonates it.

Originally Posted by DiscoJeffster

Having blown up a large car battery in my face, I can recommend against it. It sends out a lot of acid that ruins clothes and paintwork. Also, you won’t be hearing much for the following 30 minutes.

Yes I agree, the connecting earth apart from the battery is all about avoiding gas that detonates it.

Do for ding a lings like me with a second under-bonnet battery (Traxide system) those adjacent identified earth points on the inside of the front left wheel arch are probably of limited benefit?

Frankly anywhere away from the battery is ok. On other engines I've used thermostat housings, head bolts, lifting eyes. Pretty much any chunk of metal that's part of the donk, chassis or body is ok. On the D3 I've used the bracket that holds the fuel burning heater a couple of times.

Heck if your leads are long enough, you could get a decent clamp on one of the belly pan fixings. They're direct to chassis.

Originally Posted by Parso

These ones?

I have attached this to the earth point for easy connection of the jumper lead.
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Back on track - you CHARGE batt positive and earth point so the BMS keeps track of the charge.

I was always under the impression that for jump starting reason you earth at an earth point on the engine to eliminate the probability that the battery could absorb the jumping battery's 'angry pixies'.
That is, if earthed on the engine, more of the jump batteries power is more likely to get to the starter, where you want the battery power to go.

I've seen this myself many times, last time on a Ranger, where the young couple hailed me down on a main street. Was hard to get to them without partially blocking the road, so I gave the young fella the leads and I had to double park. to get them going and then his girlfriend would remove the leads of my battery and I'd move out the way. He put the leads on the battery, but his battery was completely dead and his wouldn't crank(and I have dual batts on the D1). With my D1 now blocking the road, I had to get out and see what he did, and moved lead to engine block and bam!
Very awkward situation.

I then explained to him to always earth on the engine for this reason ... and their first stop is directly to a battery place don't turn off the vehicle ... obviously battery totally stuffed.